A lot of these items are similar for anyone new to the team, not just a new college graduate.
Introduce the new team member to your team's:
- code versioning system
- code style standards
- work item / defect tracking systems
- general project layout and structure
- SDLC approach and documentation
- system documentation (whatever it may be)
- other members, and give an overview of their knowledge domains
Help them get their workstation setup and configured with the standard packages that your team uses. Help them pull down a copy of the source that they may be working on.
Set up some times to meet every other day for a few weeks and then start spacing out those meetings. The idea is to help them get up to speed with their assignments and point them in the right direction.
During those meetings go over the things that are necessary for team development but don't get emphasized as much in college. Adherence to code standards (and why); documentation of design; updates within your work item tracking system; etc..
At a very broad level, think of the basic things you need on a day to day basis and help them get started with those. Then follow through and make sure that you help show the way as the particulars come up with their first assignments.